With the recent growing tendency toward products safe to human body, various attempts have been made to relieve the actions on the skin of detergents which continuously or frequently come into contact directly with human body (for example, laundry detergents, dishwashing detergents, household detergents, hair shampoos and body cleansers). For example, there have been proposed a method which comprises regulating the pH value of a detergent composition to a weakly acidic level (pH 5 to 6) close to the pH value of human skin to thereby relieve its actions and another method which comprises using a main detergent base having an irritativeness as low as possible.
As such a low-irritative detergent base, there have been used amino acid surfactants and alkylphosphoric acid surfactants (JP-B-50-40125, JP-B-55-90335, JP-B-58-27319, etc.; the term "JP-B" as used herein means an "examined Japanese patent publication").
Although these surfactants are less irritative, they have some troubles. That is to say, they cannot always exert a sufficient detergency and foaming power when employed alone. Further, they are poor in solubility.
Regarding dishwashing detergents, it has been widely known that sodium alkylbenzenesulfonates are usable as a base with excellent detergency. However, these sodium alkylbenzenesulfonates have a disadvantage that they seriously reduce the sebum and thus cause hand skin chapping.
In recent years, therefore, dishwashing detergents containing sodium alkylethoxysulfates, which are leas irritative to the skin, as the main detergent base are employed predominantly. Moreover, these detergent bases are used together with auxiliary surfactants (for example, tertiary amine oxides, higher fatty acid diethanolamides) so as to improve the properties and establish milder actions on the skin.
Although the actions of various detergents have been relieved as discussed above, the mildness still remains unsatisfactory at present. In addition, each detergent exhibits a serious slippery feeling in use, thus giving an unpleasantness.
On the other hand, it has been known that alkylglycosides, which are less irritative sugar derivative surfactants, can not only foam per se in a stable state but also serve as a foaming stabilizer for other anionic surfactants, though they are nonionic surfactants. Thus these alkylglycosides have recently attracted public attention (JP-A-58-104625, JP-A-58-186429 and JP-A-64-69695; the term "JP-A" an used herein means an "unexamined published Japanese patent application").
The surfactant compositions and detergent compositions described in these publications are superior in various performances to the conventional ones comprising, polyoxyethylene alkyl ethers as the main base. However they have a problem that the mildness to the skin still remains unsatisfactory.
In particular, the combined use of alkylglycosides with anionic surfactants (for example, those having sulfate or sulfonate groups such as alkylbenzenesulfonates, .alpha.-olefinesulfonates, alkylsulfates, alkylethoxysulfates and .alpha.-sulfo fatty acid ester salts) is preferable from the viewpoints of detergency, foaming power and cost. In such a case, however, there inevitably arises a problem of the reduction in mildness to the skin.
The reduction in mildness to the skin, which is seemingly caused by the accelerated denaturation of proteins constituting the skin, has been regarded as a serious problem.
Although these alkylglycosides are excellent in foaming power, they give a strongly squeak feel in washing and rinsing, which brings about another technical problem that they cannot be easily employed in shampoos, etc. at the present stage.
On the other hand, amide ether carboxylates, which are known as less irritative surfactants, are marketed by CHEM-Y (Germany) under a trade name "AKYPO",
Different from the alkylglycosides, these amide ether carboxylates give no squeak feel in use. However they have a serious slippery feeling characteristic to anionic surfactants. When employed in dishwashing detergents, therefore, these amide ether carboxylates make it difficult to wash dishes due to the slippery feeling. That is to say, they cannot not always give a satisfactory feel in use. Furthermore, such an amide ether carboxylate is poor in foaming power when used alone. Because of these characteristics, these amide ether carboxylates are used in detergents only as auxiliary surfactants.
Examples of known techniques relating to the application of amide ether carboxylate surfactants to detergents include a cosmetic composition containing an amide ether carboxylate (European Patent No. 102118), a detergent composition wherein an amide ether carboxylate surfactant is used together with a polyoxyethylene alkylsulfate (European Patent No. 215504), an amide ether carboxylic acid obtained from fat and a detergent containing the same (JP-B-63-291996, European Patent No. 219893) and a detergent containing a soap as the main component together with an amide ether carboxylic acid and an alkyl ether carboxylic acid salt (U.S. Pat. No. 4,865,757). However none of these detergents is satisfactory from the viewpoint of foaming power.
On the other hand, a detergent containing an amide ether carboxylic acid and magnesium salt was described in European Patent No. 620269. However, the amide ether carboxylic acid used in the patent contains no or merely glycerol derivative. Further, the foaming power and stability of the detergent were remarkably deteriorated since this detergent contained glycerol or glyceryl ether in an amount of about 40% which is different from the composition of the present invention.
Accordingly, an object of the present invention is to provide a detergent composition having a high mildness, a good feel and high stability in use which exerts a sufficient detergency and foaming power even in the presence of a large amount of oily stains and yet causes little denaturation of skin proteins.
The present inventors have paid their attention to the high mildness of amide ether carboxylates to the skin and conducted extensive studies in order to overcome the disadvantages of the same. As a result, they have successfully found out that the above-mentioned object can be achieved by a detergent composition which contains a specific amide ether carboxylate, a specific amide ether and a specific divalent metal salt ion at a specific ratio but substantially no or little glycerol or a specific glyceryl ether.